Currently, semiconductor devices using an SOI substrate have been used as a semiconductor device capable of suppressing short-channel characteristics and variations in elements. In the SOI substrate, a buried oxide (BOX) film is formed on a supporting substrate made of high-resistance silicon (Si) and a thin layer mainly containing silicon (Si) (silicon layer or SOI layer) is formed on the BOX film.
In the case where a metal oxide semiconductor field effect transistor (MOSFET) is formed on the SOI substrate, it is possible to suppress the short-channel characteristics without introducing an impurity into a channel layer. As a result, the mobility can be improved and it is possible to suppress the variations in element due to impurity fluctuation. Thus, the improvement in integration density and operating speed in the semiconductor device and the improvement in operating margin owing to the reduction of the variations can be expected by manufacturing the semiconductor device using the SOI substrate.
Japanese Patent Application Laid-Open Publication No. 2005-504434 (Patent Document 1) describes a technique of storing information by causing breakdown of an ultra-thin dielectric between a bulk silicon substrate and a gate electrode on the bulk silicon substrate. In addition, Japanese Patent Application Laid-Open Publication No. 2005-515624 (Patent Document 2) describes a technique of forming a capacitor structure by providing an n+ region in a bulk silicon substrate below a gate electrode.